Question: In math class, the girl to boy ratio is $5$ to $4$. If there are $10$ girls, how many boys are there?
Answer: A ratio of $5$ girls to $4$ boys means that there is a group of $5$ girls for every group of $4$ boys. If there are $10$ girls, then there are $2$ groups of $5$ girls each. Because we know the ratio is $5:4$ , there must be $2$ groups of $4$ boys each. There is a total of $8$ boys in math class.